Integrated coherent optical transceiver, light engine

ABSTRACT

An coherent transceiver includes a single silicon photonics substrate configured to integrate a laser diode chip flip-mounted and coupled with a wavelength tuning section to provide a laser output with tuned wavelengths which is split in X:Y ratio partly into a coherent receiver block as local-oscillator signals and partly into a coherent transmitter block as a light source. The coherent receiver includes a polarization-beam-splitter-rotator to split a coherent input signal to a TE-mode signal and a TM*-mode signal respectively detected by two 90-deg hybrid receivers and a flip-mounted TIA chip assisted by two local-oscillator signals from the tunable laser device. The coherent transmitter includes a driver chip flip-mounted on the silicon photonics substrate to drive a pair of Mach-Zehnder modulators with 90-degree shift in quadrature-phase branches to modulate the laser output to two polarized signals with I/Q modulation and uses a polarization-beam-rotator-combiner to combine them as a coherent output signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a divisional of U.S. patentapplication Ser. No. 16/357,095, filed on Mar. 18, 2019, which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to optical telecommunication techniques.More particularly, the present invention provides a compact integratedcoherent transceiver based on silicon photonics platform, a method forforming the same, and a system having the same.

Over the last few decades, the use of communication networks exploded.In the early days Internet, popular applications were limited to emails,bulletin board, and mostly informational and text-based web pagesurfing, and the amount of data transferred was usually relativelysmall. Today, Internet and mobile applications demand a huge amount ofbandwidth for transferring photo, video, music, and other multimediafiles. For example, a social network like Facebook processes more than500 TB of data daily. With such high demands on data and data transfer,existing data communication systems need to be improved to address theseneeds.

40-Gbit/s and then 100-Gbit/s data rates wide-band DWDM (DenseWavelength Division Multiplexed) optical transmission over existingsingle-mode fiber is a target for the next generation of fiber-opticcommunication networks. Chip-scale widely-tunable lasers have been ofinterest for many applications such as wide-band DWDM communication andwavelength-steered light detection and ranging (LIDAR) sensing. Morerecently, optical components are being integrated on silicon (Si)substrates for fabricating large-scale photonic integrated circuits thatco-exist with micro-electronic chips. a whole range of photoniccomponents, including filters, (de)multiplexers, splitters, modulators,and photodetectors, have been demonstrated, mostly in thesilicon-on-insulator (SOI) platform. The SOI platform is especiallysuited for standard DWDM communication bands at 1300 nm and 1550 nm, assilicon (n=3.48) and its oxide SiO₂ (n=1.44) are both transparent, andform high-index contrast, high-confinement waveguides ideally suited formedium to high-integration planar integrated circuits (PICs).

Coherent optical fiber communications were studied extensively in the1980s mainly because high sensitivity of coherent receivers couldelongate the unrepeated transmission distance; however, their researchand development have been interrupted for nearly 20 years behind therapid progress in high-capacity wavelength-division multiplexed (WDM)systems using erbium-doped fiber amplifiers (EDFAs). Not long ago, thedemonstration of digital carrier phase estimation in coherent receivershas stimulated a widespread interest in coherent optical communicationsagain. The fact is, the digital coherent receiver enables us to employ avariety of spectrally efficient modulation formats such as M-ary phaseshift keying (PSK) and quadrature amplitude modulation (QAM) withoutrelying upon a rather complicated optical phase-locked loop. Inaddition, since the phase information is preserved after detection, wecan realize electrical post-processing functions such as compensationfor chromatic dispersion and polarization-mode dispersion in the digitaldomain. These advantages of the coherent receiver have enormouspotential for innovating existing optical communication systems.

Coherent transmitter has a TE and TM path. Silicon photonics chip,however, operates essentially only in a TE only configuration. Severaltechnical challenges exist for making polarization-independent orwavelength tunable passive and active components as well as integratingthese components to form a coherent optical transceiver in a compactsilicon photonics platform. Therefore, improved techniques and methodsof forming an integrated compact coherent transceiver are desired.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to optical telecommunication techniques.More particularly, the present invention provides an integrated compactcoherent transceiver in silicon-photonics platform. Merely by example,the present invention discloses a coherent transmitter block including apolarization independent semiconductor optical amplifier (SOA) coupledvia polarization beam rotator combiner (PBRC) to a driver electronicschip with both in-phase and quadrature-phase modulations of broadbandsignals from an independently packaged wide-band tunable laser withsilicon-photonics tuning section, and a coherent receiver blockincluding polarized hybrid receivers converting TE-polarized opticalsignals split by a polarization beam splitter rotator (PBSR) toelectrical signals for a transimpedance amplifier (TIA) electronicschip, and a method of integrating these components to form a coherenttransceiver in a compact silicon photonics platform for wide-band DWDMoptical communications, though other applications are possible.

In modern electrical interconnect systems, high-speed serial links havereplaced parallel data buses, and serial link speed is rapidlyincreasing due to the evolution of CMOS technology. Internet bandwidthdoubles almost every two years following Moore's Law. But Moore's Law iscoming to an end in the next decade. Standard CMOS silicon transistorswill stop scaling around 5 nm. And the internet bandwidth increasing dueto process scaling will plateau. But Internet and mobile applicationscontinuously demand a huge amount of bandwidth for transferring photo,video, music, and other multimedia files. This disclosure describestechniques and methods to improve the communication bandwidth beyondMoore's law.

With the increase in the transmission capacity of WDM systems, coherenttechnologies attracted a renewal of widespread interest after 2000. Themotivation is to develop methods for meeting the ever-increasingbandwidth demand with multi-level modulation formats based on coherenttechnologies. The first step in the revival of coherent opticalcommunications research was triggered by quadrature phase-shift keying(QPSK) modulation/demodulation experiment featuring optical in-phase andquadrature (IQ) modulation (IQM) and optical delay detection. In such ascheme, we can double the bit rate while maintaining the symbol rate,and a 40-Gb/s differential QPSK (DQPSK) system has been put intopractical use. Coherent transmitter has a transverse electric (TE) modeand transverse magnetic (TM) mode path. Silicon photonics chip operatesessentially only in a TE only configuration. The signal has both TE modeand TM mode parts. To accomplish a silicon-photonics based integrationof coherent transceiver, we need to have at least the following twocomponents on the silicon photonics chip: 1) Polarization Beam RotatorCombiner (PBRC) integrated with a polarization-independent semiconductoroptical amplifier (SOA) and driver in the coherent transmitter and 2)Polarization Beam Splitter Rotator (PBSR) integrated with electronicslike transimpedance amplifier (TIA) in the coherent receiver, and tointegrate the coherent transmitter and receiver with a tunable laserprovided in a flip-chip.

In an embodiment, the present invention provides a tunable laser devicebased on silicon photonics. The tunable laser device includes asubstrate configured with a patterned region comprising one or morevertical stoppers, an edge stopper facing a first direction, a firstalignment feature structure formed in the patterned region along thefirst direction, and a bond pad disposed between the vertical stoppers.The tunable laser device further includes an integrated coupler built inthe substrate located at the edge stopper. Additionally, the tunablelaser device includes a laser diode chip including a gain region coveredby a P-type electrode and a second alignment feature structure formedbeyond the P-type electrode, the laser diode chip being flipped to restagainst the one or more vertical stoppers with the P-type electrodeattached to the bond pad and the gain region coupled to the integratedcoupler. Furthermore, the tunable laser device includes a tuning filterfabricated in the substrate and coupled via a wire waveguide to theintegrated coupler.

In a specific embodiment, the present invention provides a coherenttransceiver integrated on silicon photonics substrate. The coherenttransceiver includes a substrate member and a tunable laser devicecomprising a laser diode chip having a gain region with a p-sideelectrode flipped down and mounted on the substrate member. The gainregion is coupled with a wavelength tuning section formed in thesubstrate member to tune wavelengths of a laser light outputted from thegain region to a waveguide in the substrate member. The coherenttransceiver further includes a first power splitter coupled to thewaveguide to split the laser light to a first light and a second light.Additionally, the coherent transceiver includes a coherent receiverblock including at least two 90° hybrid receivers coupled respectivelyto two outputs of a polarization beam splitter rotator in the substratemember to receive a coherent input signal from a coherent opticalnetwork. The coherent transceiver also is configured to have the two 90°hybrid receivers to couple with two outputs of a second power splitterto receive two local-oscillator signals split from the first light forassisting detections of a transverse electric (TE) mode signal and atransverse magnetic (TM) mode signal in the coherent input signal.Furthermore, the coherent transceiver includes a coherent transmitterblock including at least a pair of in-phase/quadrature-phase modulatorsin the substrate member to respectively modulate two parts split fromthe second light to two I/Q-modulated signals in TE-mode, a polarizationbeam rotator combiner in the substrate member to rotate one of the twoI/Q modulated signals to a TM-mode signal and combine with the other oneof two I/Q modulated signals in TE-mode to generate a coherent outputsignal transmitted through a polarization-independent semiconductoroptical amplifier to the coherent optical network.

In another specific embodiment, the present invention provides a packageof an integrated coherent optical transceiver. The package includes ametal case having two side members joint by a joint member coupled witha bottom member and clipped with a lid member. The package furtherincludes a printed circuit board (PCB) disposed on the bottom memberwith multiple electrical pins located near a back end of the metal caseand a silicon photonics substrate with a board grid array at bottommounted on the PCB. Additionally, the package includes a coherenttransceiver chip integrated on the silicon photonics substrate includingone input port and one output port respectively disposed on a front endof the metal case and coupled to the silicon photonics substrate via afirst fiber and a second fiber. The coherent transceiver chip includesfurther a tunable laser device including two laser diode chips coupledwith a wavelength tuning section embedded in a first region of thesilicon photonics substrate and configured to output a laser light.Furthermore, the coherent transceiver chip includes a transimpedanceamplifier (TIA) chip flip-mounted on a second region of the siliconphotonics substrate and a driver chip flip-mounted on a third region ofthe silicon photonics substrate. Moreover, the coherent transceiver chipincludes a silicon photonics circuit formed in a fourth region of thesilicon photonics substrate. The silicon photonics circuit is configuredto couple with the first fiber to receive a coherent input light signaland to couple with the tunable laser device to receive a first portionof a laser light as local oscillator signals to assist detections ofboth TM-mode and TE-mode light signals in the coherent input lightsignal by the TIA chip. The silicon photonics circuit is also configuredto use the driver chip to drive modulations of a second portion of thelaser light to generate a coherent output light signal outputted to thesecond fiber.

In another specific embodiment, the present invention provides a lightengine device including an optical coherent transceiver integrated on asemiconductor substrate member. The light engine device includes asubstrate member comprising a surface region. The light engine devicefurther includes an optical input configured to an incoming fiber deviceand an optical output configured to an outgoing fiber device.Additionally, the light engine device includes a transmit path providedon the surface region. The transmit path includes a polarizationindependent optical amplifier device coupled to the optical output. Thetransmit path also includes a polarization beam rotator combiner devicecoupled to the polarization independent optical amplifier and coupled tothe optical output. The transmit path further includes a dualpolarization I/Q Mach Zehnder modulator device coupled to thepolarization beam rotator combiner device and coupled to the opticaloutput. The transmit path again includes a driver device coupled to thedual polarization I/Q Mach Zehnder modulator device and configured todrive an electrical signal to the dual polarization I/Q Mach Zehndermodulator. Furthermore, the transmit path includes a tunable laserdevice comprising a laser diode chip having a gain region with a p-sideelectrode flipped down and mounted on the substrate member. The gainregion is coupled with a wavelength tuning section formed in thesubstrate member to tune wavelengths of a laser light outputted from thegain region to a waveguide in the substrate member. Moreover, thetransmit path includes a first power splitter coupled to the waveguideto split the laser light to a first light and a second light. The secondlight is coupled to the dual polarization I/Q Mach Zehnder modulatordevice. Further, the light engine device also includes a receive pathprovided on the surface region. The receive path includes a second powersplitter coupled to the first light. The receive path further includes apair of 90° hybrid receivers. Each of the pair of 90° hybrid receiversincludes a photo detector device and a hybrid mixer device, coupledrespectively to two outputs of a polarization beam splitter rotator inthe substrate member to receive the optical input and to two outputs ofthe second power splitter to receive the first light from the tunablelaser device for assisting detections of a transverse electric (TE) modesignal and a transverse magnetic (TM) mode signal in the coherent inputsignal. Furthermore, the receive path includes a transimpedanceamplifier coupled to each of the 90° hybrid receivers and coupled toeach of the photo detector devices that convert a combination of thefirst light with the optical input into an electrical signal to betransmitted to using the transimpedance amplifier device. The lightengine device further includes a heterogeneous integration configuredusing the substrate member, the transmit path, and the receive path toform a single silicon photonics device.

The present invention achieves these benefits and others in the contextof known waveguide laser modulation technology. However, a furtherunderstanding of the nature and advantages of the present invention maybe realized by reference to the latter portions of the specification andattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this process andscope of the appended claims.

FIG. 1 is a simplified block diagram of a coherent optical transceiveraccording to an embodiment of the present invention.

FIG. 2A is a top-view diagram of a waveguide-based polarization beamsplitter-rotator (PBSR) or polarization beam rotator-combiner (PBRC)according to an embodiment of the present invention.

FIG. 2B is a cross-section view along AA′ plane of the waveguide-basedPBSR or PBRC of FIG. 2A according to an embodiment of the presentinvention.

FIG. 2C is a cross-section view along BB′ plane of the waveguide-basedPBSR or PBRC of FIG. 2A according to an embodiment of the presentinvention.

FIG. 2D is a cross-section view along CC′ plane of the waveguide-basedPBSR or PBRC of FIG. 2A according to an embodiment of the presentinvention.

FIG. 3 is a simplified diagram of a silicon photonics tunable laserdevice according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a perspective view a laser diodechip flipped bonding to a silicon photonics substrate according to anembodiment of the present invention.

FIG. 5 is an exemplary diagram of a wavelength tuning map of a siliconphotonics tunable laser according to an embodiment of the presentinvention.

FIG. 6 is a simplified diagram of a silicon photonics tunable laserdevice according to another embodiment of the present invention.

FIG. 7 is a flowchart of a method for tuning wavelength of a laseroutput of the silicon photonics tunable laser device according to anembodiment of the present invention.

FIG. 8 is an exemplary diagram of two superimposed transmission spectraof respective two ring resonators with different radii of a tunablefilter in the silicon photonics tunable laser device according to anembodiment of the present invention.

FIG. 9 is an exemplary diagram of a reflectivity spectrum of a reflectorcoupled to the two ring resonators of the tunable filter according tothe embodiment of the present invention.

FIG. 10 is a simplified block diagram of the tunable filter includingtwo ring resonators, a reflector, plus a phase shifter in a Vernier ringreflector configuration according to an embodiment of the presentinvention.

FIG. 11 is an exemplary diagram of two synthesized spectra respectivelycorresponding to wavelengths being tuned from 1555 nm to 1535 nm bytuning the tunable filter in Vernier ring reflector configuration andcorresponding gain profile from 1530 nm to 1570 nm according to theembodiment of the present invention.

FIG. 12 is an exemplary diagram of laser spectra outputted by thesilicon photonics tunable laser device with laser wavelength being tunedfrom 1555 nm to 1535 nm according to an embodiment of the presentinvention.

FIG. 13 is a schematic diagram of three types of an integrated couplerbased on SiN in Si waveguide according to some embodiments of thepresent invention.

FIG. 14A is an exemplary diagram of a relationship between coupling lossand a lateral misalignment for an integrated coupler coupled between thetunable filter and a laser diode chip according to an embodiment of thepresent invention.

FIG. 14B is an exemplary diagram of a relationship between coupling lossand a vertical misalignment for the integrated coupler coupled betweenthe tunable filter and a laser diode chip according to the embodiment ofthe present invention.

FIG. 15A is a perspective view of an integrated coherent opticaltransceiver on a silicon photonics substrate according to an embodimentof the present invention.

FIG. 15B is a side view of the integrated coherent optical transceiveron a silicon photonics substrate of FIG. 15A according to an embodimentof the present invention

FIG. 16A is a schematic diagram of an open package of an integratedcoherent optical transceiver according to an embodiment of the presentinvention.

FIG. 16B is a schematic diagram of a closed package of the integratedcoherent optical transceiver of FIG. 16A according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to optical telecommunication techniques.More particularly, the present invention provides an integrated compactcoherent transceiver in silicon photonics platform. Merely by example,the present invention discloses a coherent transmitter block including apolarization independent semiconductor optical amplifier (SOA) coupledvia polarization beam rotator combiner (PBRC) to a driver electronicschip and to an independently packaged wide-band tunable laser withsilicon photonics tuning section, and a coherent receiver blockincluding polarized hybrid receivers coupled to transimpedance amplifier(TIA) electronics chip via polarization beam splitter rotator (PBSR),and a method of integrating these components to form a coherenttransceiver in a compact silicon photonics platform for wide-band DWDMoptical communications, though other applications are possible.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

In an aspect, the present disclosure provides a compact integratedcoherent transceiver based on silicon photonics platform. As datatransmission-capacity increase in WDM systems, coherent technologieswith polarized optical signals also increasingly attract more and moreinterest over the recent years with motivation of meeting theever-increasing bandwidth demand using multilevel modulation formats.For example, a digital signal transmitting/receiving scheme is developedfor coherent transmission system supported with a quadrature PSK (QPSK)modulation/demodulation featuring optical in-phase and quadrature (I/Q)modulation and optical delay detection. In such a scheme, one symbolcarries two bits by using the four-point constellation on the complexplane, therefore, the bit rate is doubled, while keeping the symbolrate, or maintaining the bit rate even with the halved spectral width torealize a large capacity of 100 Gbit/s and more than 100 Gbit/s perchannel. Optical coherent I/Q modulation can be realized withMach-Zehnder (MZ) type push-pull modulators in parallel, between which aπ/2-phase shift is given. The I/Q components of the optical carrier ismodulated independently with the coherent I/Q modulator, enabling anykind of modulation formats.

FIG. 1 shows simplified block diagram of an integrated coherent opticaltransceiver according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown, the integratedcoherent optical transceiver is configured to integrate asilicon-photonics-based tunable laser 1000 with a coherent transmitterblock 2000 and a coherent receiver block 3000 on a single siliconphotonics substrate 100. Optionally, the tunable laser is a wide-bandlaser source with its output optical signal tunable over entire C-bandor O-band. The wavelength tuning is achieved using a silicon photonicstuning section including a heater-tuned micro-ring resonator filterbuilt in the silicon photonics substrate 100 while a laser diode chipwith an InP gain region with p-side flip down mounted onto the siliconphotonics substrate 100. Particularly, through the silicon photonicstuning section and a waveguide-based wavelength locker, laser wavelengthcan be tuned to provide all ITU channels in C-band each with a sharptransmission spectrum for DWDM communication. More details can be founddescriptions of FIG. 3 through FIG. 14 of the specification. Optionally,the laser light is outputted from the InP gain region coupled via anintegrated coupler with a waveguide (formed in a same silicon photonicssubstrate 100). The waveguide delivers the laser light, which is used asa local oscillator source for the coherent receiver 3000 to detectincoming coherent light signals and is also served as a light source forproducing I/Q modulated coherent signal to be transmitted by thecoherent transmitter 2000.

Optionally, the integrated coherent optical transceiver includesmultiple silicon waveguides respectively laid in the silicon photonicssubstrate 100, though they are not explicitly labeled in FIG. 1, forconnecting several different silicon photonics components includingpower splitter, polarization beam splitter and rotator, polarizationbeam rotator and combiner, phase shifter, power attenuator, or part ofoptical modulator. Optionally, the silicon waveguides have regularrectangular wire shape with a fixed width and height. Optionally, theheight is selected based on a usage of standard 220 nmsilicon-on-insulator (SOI) substrate during its formation process.Optionally, the width of the silicon waveguide is about 300 nm to 500nm. Optionally, the silicon waveguides have alternative shapedstructures like rib structure with multiple steps in height, taperstructure with varying widths along its length, or multiple branches ofdifferent widths and separations joined at different cross-sectionplanes, depending on specific functional applications. Optionally, someof the silicon photonics components mentioned above are also siliconwaveguides themselves monolithically formed in a same manufactureprocess for preparing the silicon photonics substrate 100 to integratethe coherent optical transceiver.

For ultrasmall silicon waveguides of a few hundred of nanometers inwidth (parallel to the substrate) and height (orthogonal to thesubstrate) used in compact silicon photonics modules, they often exhibitvery strong polarization dependence for a transmitted light withinfrared wavelength (typical for telecommunications) such that thetransmission loss for a transverse electric (TE) mode polarization(parallel to the substrate) is much less than that for a transversemagnetic (TM) mode polarization (orthogonal to the substrate).Therefore, typical silicon photonics device works for TE mode only.Optionally, the output light of the tunable laser 1000 in a transverseelectric (TE) mode polarization is split between the transmitter block2000 and the receiver block 3000 with an optimized ratio. In thetransmitter block 3000, the light coming from the tunable laser 1000 ata wavelength selected in a broadband by a tunable filter section isfirstly split to a TE-mode light and a TM*-mode (still a TE-mode) light,both of which are performed an optical I/Q modulation. The TE-mode lightbecomes a TE-mode signal. The TM*-mode light is then performed apolarization rotation to form a transverse magnetic (TM) mode signal.The TE-mode signal and the TM-mode signal are then combined to become acoherent output signal of the transceiver at the selected wavelength. Inthe receiver block 3000, the optical signal (TE-mode) coming from thetunable laser 1000 acts as a local oscillator at the wavelength selectedby the tunable filter section for detecting incoming coherent inputsignals.

Referring to FIG. 1, the output of the tunable laser 1000 issubstantially a TE-mode laser light, which is firstly split by a powersplitter 1001 to two parts, a first light and a second lightrespectively with a X:Y ratio. The first light is delivered to thecoherent receiver block 3000 with X portion of the laser power and thesecond light is forwarded to the coherent transmitter block 2000 with Yportion of the laser light. The X:Y ratio is varied or optimized basedon specific system operation condition. Optionally, X is set in a rangefrom 10 to 50%. For the first light coupled into the coherent receiverblock 3000, it is further split to two 50% portions, a third light and afourth light, by a power splitter 3001. The third light is loaded into aTE 90° hybrid receiver 3200 and the fourth light is loaded into a TM*90° hybrid receiver 3300, for respectively assisting detections ofTE-mode/TM-mode signals of the incoming optical signal received by thecoherent optical transceiver via an input port (Light in).

For the second light coupled into the coherent transmitter block 2000,it is used as an original light source to generate a coherent opticalsignal to be transmitted out of an output port. Optionally, the secondlight can be provided as a TE-mode polarized light and tuned to be atany wavelength in a broadband like C-band or O-band designated fortelecommunication. In order to serve as a coherent light signal withmixed polarization modes, a TM-mode polarized part of the second lightneeds to be generated. Both TE- and TM-mode polarized parts aremodulated by optical coherent modulators. Optionally, the opticalcoherent I/Q modulator based on delay-line interferometer in silicon orsilicon nitride or similar material integrated in silicon photonicssubstrate has been developed with polarization compensation at selectivewavelengths, e.g., as shown in U.S. Pat. No. 10,031,289, assigned toInphi Corp.

As seen in FIG. 1, both the coherent transmitter block 2000 and thecoherent receiver 3000 of the integrated coherent optical transceiverhave a TE-mode path and a TM-mode path for providing or detecting acoherent light with mixed polarizations in the polarization-independentcommunication system. However, silicon photonics circuit includingSi-based waveguide linear modulator operates essentially in a TE-modeonly configuration. In order to handle the coherent optical signal withboth TE mode and TM mode parts, the silicon-photonics based coherenttransceiver needs at least 1) a Polarization Beam Rotator Combiner(PBRC) integrated with a polarization-independent semiconductor opticalamplifier (SOA) at an output port (Light out) of the transmitter blockto output a coherent optical signal having both TE and TM mode, and 2) aPolarization Beam Splitter Rotator (PBSR) to split TE-mode part andTM-mode part of the incoming coherent optical signal and rotate theTM-mode part to TE-mode before being coupled into optical hybriddetectors.

Conventional PBSR is either wavelength sensitive so that it is not suitfor broadband operation or based on prism that is hard to be made insuper compact size. A compact PBSR based on photonic integrated circuits(PICs) having combined features like compact size, high extinctionratio, low insertion loss, broadband range, stability, simple structureand high tolerances in manufacture has been developed, referring to U.S.Pat. No. 9,915,781 assigned to Inphi Corp. In particular, as shown inFIG. 2A, a waveguide-based polarization beam splitter-rotator is shownin its top view. The PBSR 16 includes a single piece of monolithicallysilicon planar waveguide including multiple shaped sections formed witha standard 220 nm silicon layer of a silicon-on-insulator (SOI)substrate. A first section is a converter in rib structurecharacterized, in both FIG. 2A and FIG. 2B, by a top-layer 1602overlying a bottom-layer 1601 extended in the lengthwise directionthrough a first segment of a length L₁ from the input port 1600 to ajoint plane AA′ and a second segment of a length L₂ from the joint planeto the first cross-section plane 1610. The top-layer 1602 is narrowerthan the bottom-layer 1601 and both vary throughout the first length L₁and throughout the second length L₂ except they have a first commonwidth W₀ at the input port 1600 and a second common width W₁ at thefirst cross-section plane 1610. The specific length-width combination ofboth the top-layer 102 and the bottom-layer 1601 is configured toprovide a polarization-mode conversion of TM-mode to TE-mode for acoherent light wave transmitted through, depending on wavelength rangesof the coherent optical signal.

The top-layer 1602 of a thickness of h_(t) is formed overlying thebottom-layer 1601 of a thickness h_(b) in an overlay process after thesilicon layer of the thickness of h=h_(t)+h_(b)=220 nm over an oxidelayer is patterned for the rib structure waveguide as part of amonolithic process of forming the PBSR 16. In a specific embodiment, theconverter is configured for handling optical wave of broadbandwavelengths, for example, O-band in a range of 1270 nm to 1330 nm orC-band from about 1530 nm to about 1560 nm (with slightly differentdimensions of the rib structure). In addition, the width W_(t) of thetop-layer 1602 at the joint plane is made to be greater than the firstcommon width W₀, the width W_(b) of the bottom-layer 1601 at the jointplane is made to be greater than the width W_(t) of the top-layer 1602but smaller than the second common width W₁, and the first length L₁ ismade to be shorter than the second length L₂. After fine tuning thelength-width combination (with a standard height of 220 nm) under theabove configuration the rib structure waveguide serves a desiredpolarization mode converter. For an input light with mixed TM mode andTE mode inputted via the input port 1600, the TM mode is substantiallyconverted to first-order Transverse Electric (TE1) mode and the TE modeis substantially converted to zero-order Transverse Electric (TE0) modeas the input light travels to the first cross-section plane 1610.Specifically, the TE1 mode includes two sub-modes, an out-of-phase T1 ₁sub-mode and an in-phase TE1 ₂ sub-mode. The TE0 mode just is asingle-phase mode.

Referring to FIG. 2A, a second shaped section of the PBSR 16 includes asplitter 1612 directly coupled to the first cross-section plane of theconverter as part of the monolithic planar silicon waveguide formed fromthe 220 nm silicon layer of the SOI substrate. FIG. 2C is across-section view of the waveguide-based PBSR 10 along BB′ planeaccording to an embodiment of the present invention. Referring to FIG.2C and FIG. 2A, the splitter 1612 is a planar waveguide having a heighth of the 220 nm silicon layer extended in the lengthwise direction fromthe first cross-section plane 1610 to a second cross-section plane 1620.The first cross-section plane 1610 passes the input light transmittedthrough the converter. The second cross-section plane 1620 includes afirst port 1701 and a second port 1702 respectively located next to twoopposing edges and separated from each other by a gap W_(g). In anembodiment, the splitter 1612 is designed for splitting the input lightreceived at the first cross-section plane 1610 substantially evenly to afirst wave at the first port 1701 and a second wave at the second port1702.

Referring to FIG. 2A again, a third shaped section of the PBSR 16includes a phase shifter waveguide coupled to or naturally extended fromthe first port 1701 and the second port 1702 at the second middlecross-section plane 1620. The phase shifter waveguide includes a firstwaveguide arm 121 coupled to the first port 1201 and a second waveguidearm 122 coupled to the second port 1202, both having the same height hof the 220 nm silicon layer. The first waveguide arm 1621 is extended inthe lengthwise direction to a third port 1801 of a third cross-sectionplane 1630 and the second waveguide arm 1622 is separately extended inthe lengthwise direction to a fourth port 1802 of the thirdcross-section plane 1630. In an embodiment, the first waveguide arm 1621is configured to receive the first wave from the first port 1701 and totransmit the first wave through at least a length L₆ towards the thirdport 1801 while keeping the first wave at the third port 1801 in-phaserelative to that at the first port 1701. The second waveguide arm 1622is configured to receive the second wave from the second port 1702 andto transmit the second wave through a separate path of the same lengthL₆ towards the fourth port 1802 while adding a phase shift to the secondwave at the fourth port 1802 relative to that at the second port 1702.

FIG. 2D is a cross-section view of the waveguide-based PBSR 16 of FIG.2A along CC′ plane according to an embodiment of the present invention.Referring to FIG. 2A and FIG. 2D, the first waveguide arm 1621 of thephase shifter includes a straight bar shape of at least the length L₆and a first arm width W_(1a) connected between the first port 1701 andthe third port 1801, and the second waveguide arm 1622 of the phaseshifter includes a straight bar shaped portion having at least thelength L₆ joined aside with a triangle shaped portion connected betweenthe second port 1702 and the fourth port 1802. The second waveguide arm1622 has a varying second arm width W_(2a) which increases from thefirst arm width W_(1a) at one end to a maximum at an apex of thetriangle shaped portion then decreasing again to the first arm widthW_(1a) at the other end. The constant width W_(1a) associated with thelength L₆ in the first waveguide arm 1621 effectively retains first wavein-phase travelling through the first waveguide arm 1621 to reach thethird port 1801 at the third cross-section plane 1630. At the same time,the varying width W_(2a) associated with the length L₆ in the secondwaveguide arm 1622 can be adjusted to provide a desired phase delay tothe second wave traveling independently through the second waveguide arm1622 to reach the fourth port 1802 at the third cross-section plane1630. In a specific configuration, the maximum W_(2a) is set to beslightly smaller than twice of the first arm width W_(1a) and the lengthL₆ is no greater than 11 μm to cause a phase delay of (½)π in the secondwave through the second waveguide arm 1622. Alternatively, with lightlyreduction in the maximum W_(2a) and increase in the length L₆, a phasedelay of (3/2)π can be produced to the second wave through the secondwaveguide arm 1622. In principle, a phase shift of (π/2+nx) can begenerated for n being any integer though effective phase values are alllimited within 2π.

Referring to FIG. 2A again, a fourth shaped section of the PBSR 16includes a 2×2 MMI coupler 1632 as a planar waveguide of the same heighth of 220 nm silicon layer naturally extended from the third port 1801and the fourth port 1802 at the third cross-section plane 1630 to anoutput plane 1640 with a first output port 1901 and a second output port1902. From the input port 1600 to the fourth cross-section plane 1640,the PBSR 16 includes a total length less than 100 μm, thus forming avery compact sized device suitable for highly integrated siliconphotonics communication system. The 2×2 MMI coupler 1632 ischaracterized by a rectangular shape of a length L₇ measured from thethird cross-section plane 1630 to the output plane 1640 and a width W₂.The first output port 1401 is aligned with the third port 1801 in a barposition at a distance W_(p) away from a central line of the rectangularshaped planar waveguide in the lengthwise direction. The first outputport 1901 is in a cross position relative to the fourth port 1802. Thesecond output port 1902 and the fourth port 1802 are respectively inmirror symmetric positions relative to the first output port 1901 andthe third port 1801, nevertheless making the second output port 1902 tobe in a cross-position relative to the third port 1801. The 2×2 MMIcoupler 1632 in such configuration induces a general interference ofoptical waves coupled via both the third port 1801 and the fourth port1802 and outputs a first output light in TE0 mode to the first outputport 1901 and a second output light in TE0 mode to the second outputport 1902. Depending on specific polarization modes and phase differenceof the first wave at the third port 1801 and the second wave at thefourth port 1802, optionally, the first output light may be exclusivelyoriginated from the input light with TM mode and the second output lightmay be exclusively originated from the input light with TE mode. Inother words, the PBSR 16, with a compact length less than 100 μm, isable to split the input light with mixed TM mode part and TE mode part,and to guide substantially TM mode part and rotate it to a TE0 modeoutputted to a first output port, and guide substantially TE mode partand retain it as TE mode outputted to a second output port, realizing apolarization splitting/rotating function. And this function isapplicable to broadband transmission with any wavelength in entireO-band or C-band.

Referring back to FIG. 1, for the coherent receiver block 3000 theincoming coherent light signal R has mixed TE/TM-mode parts in I/Qmodulation. A PBSR 3100 is used to receive the incoming light signal Rand, following the polarization splitting/rotating function describedabove, to output the TE-mode part signal RE to a first waveguide in TEpolarization and the TM-mode part R_(M) to a TM*-branch also in TEpolarization, compatible for the silicon photonics chip that operates inthe TE-mode only. The TE-mode part signal R_(E) in the TE-branch is thenloaded into a TE 90° hybrid receiver 3200 which also receives alocal-oscillation (LO) signal A in TE-mode split from the tunable laser1000 as a second input (FIG. 1). The TE 90° hybrid receiver 3200produces four outputs: ½×(R_(E)+A), ½×(R_(E)−A), ½×(R_(E)+jA), and½×(R_(E)−jA) through a perfect I/Q demodulation, into a trans-impendenceamplifier (TIA) chip 3400 where these optical signals are converted totwo current signals I_(I) and I_(Q) by balanced photodetectors. Further,the TIA chip includes analog-to-digital converter to convert the currentsignals into digital signals that can be processed in a digital signalprocessor (DSP) (not explicitly shown) and the TE-mode part signal ofthe incoming coherent light can be specifically detected. Similarly, theTE-mode part signal R_(M) in the TM*-branch is loaded into a TM* 90°hybrid receiver 3300 which is also receives a LO signal A in TE-modesplit from the tunable laser 1000 as a second input. Also, the outputsof the TM* 90° hybrid receiver 3300 are sent to the TIA chip 3400 wherethe TM-mode part signal of the incoming coherent light can bespecifically detected via I/Q demodulation. Optionally, the TIA chip3400 is a flip-chip mounted on the silicon photonics substrate 100shared with the silicon photonics chip including the PBSR 3100 and powersplitter 3001.

Referring to FIG. 1 again, the coherent transmitter block 2000 receivesthe Y portion light in TE-mode split from the tunable laser 1000 whichis non-modulated and needs optical I/Q modulation for coherentcommunications. In the embodiment, the coherent transmitter block 2000includes a driver chip 2600 configured to provide bias voltages anddigital transmit electrical signals for an optical modulator to modulatethe input light from the tunable laser 1000. The driver chip 2600 (e.g.,including a serializer, a 4-level encoder, a 2-bit digital-to-analogconverter) is provided in a flip-chip mounted on the same siliconphotonics substrate 100. Optionally, the driver chip 2600 and the TIAchip 3400 can be integrated into a single chip. In the embodiment, acoherent I/Q modulator based on delay-line interferometer made bysilicon or silicon nitride or similar material integrated in the siliconphotonics chip that shares the same silicon photonics substrate 100 withthe coherent receiver block 3000. The Y portion light in TE-mode fromthe tunable laser 1000 is split to a first input light in a TE Branch2501 and a second input light in a TM* Branch 2502. Here the split ofthe Y portion light is done via a 50:50 power splitter (not explicitlyshown) while retaining its TE polarization in either branch. Each of thefirst input light and the second input light is coupled into an I/Qmodulator. In the embodiment, a first I/Q modulator is configured tohave four linear waveguide arms with different phase delays to receivefour equally split portions of the first input light by three powersplitters in two stages. A first pair of arms form an in-phase (I)branch in Mach-Zehnder modulation configuration that produces a firstoutput with in-phase modulation components for the first input lightinto the TE Branch 2501. A second pair of arms form a quadrature phase(Q) branch also in Mach-Zehnder modulation configuration plus a 90°phase shifter 2401 that generates a second output with quadrature phasemodulation components for the first input light into the TE Branch 2501.As the first output and the second output are combined, a TE-mode outputlight with four-level I/Q modulation of the first input light isgenerated in a TE-output line 2503. Additionally, in the embodiment, asecond I/Q modulator is configured, substantially the same as the firstI/Q modulator, to have four linear waveguide arms with different phasedelays to receive four equally split portions of the second input lightinto the TM* Branch 2502 by three power splitters in two stages.Similarly, a 90° phase shifter 2402 is used to combine the In-Phase andQuadrature components (I and Q) to generate a TM*-mode output light withfour-level I/Q modulation of the second input light in a TM*-output line2504. Note, this TM*-mode output light still a TE-mode light originatedfrom the tunable laser 1000, even though it is labeled as TM*.

Since the output light in both TE-output line and TM*-output line is TEmode, a polarization beam rotator combiner (PBRC) to combine them at theoutput to form a coherent optical signal. Referring to FIG. 1, thecoherent transmitter block 2000 also includes a PBRC 2200 to rotate theTE-mode light in the TM*-output line 2504 to a TM-mode light combiningwith the TE-mode light in the TE-output line 2503. Optionally, a TEattenuator 2301 and a TM* attenuator 2302 are two variable opticalattenuators respectively inserted into the TE-output line 2503 and theTM*-output line 2504 to tune the polarization-dependent power loss inthe two branches before the PBRC 2200. The output of the PBRC 2200 is afully coherent optical signal with mixed TE/TM modes in I/Q modulation.The output is then fed to the polarization independent semiconductoroptical amplifier (SOA) 2100 to boost optical power of the coherentoptical signal being transmitted out of the coherent transceiver.Optionally, residual polarization dependent gain in the polarizationindependent SOA 2100 can also be tuned with the variable opticalattenuators 2301 and 2302 in the TE and TM* paths. Optionally, the useof the polarization-independent SOA 2100 at the output of the coherenttransmitter block 2000 allows for wide range of output power from thecoherent optical transceiver no matter the polarization state of theoptical signal. Optionally, the polarization-independent SOA 2100 isprovided as a flip-chip mounted on the silicon photonics substrate 100.The flip-chip mounting of the SOA 2100 is similar to flip-chipintegrations of the drive chip 2600 and the TIA chip 3400 with thesilicon photonics substrate 100.

Optionally, the PBRC 2200 is substantially a same type ofsilicon-photonics device of the PBSR 3100 worked with reversed opticalpaths. In particular, referring to FIG. 2A, two TE-mode light waves,e.g., a TE-mode light with I/Q modulation and a TM*-mode light with I/Qmodulation, are respectively loaded to two input ports 1901 and 1902 ofthe PBRC (which are two output ports for a PBSR). The TE-mode lightloaded into the cross port 1901 is kept at the TE-mode at an output port1600 of the PBRC (which is an input port for the PBSR), while theTM*-mode light (also a TE-mode light) loaded in a bar port 1902 isrotated by 90 degrees to become a true TM-mode polarization at theoutput port 1600.

FIG. 3 is a simplified diagram of a silicon photonics tunable laserdevice according to an embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown, a siliconphotonics tunable laser device 10 includes a laser diode flip-chip 400,a tunable filter 200, and integrated couplers 301 and 302, all of thembeing integrated into a single silicon photonics substrate 100. Thesilicon photonics substrate 100 includes a patterned region 110pre-fabricated with one or more vertical stoppers 112 and 113, aplurality of alignment features 114, 115 substantially distributed alonga first direction z, and a bond pad 111 laid substantially between theone or more vertical stoppers 112 and 113. The patterned region 110,optionally, is configured to be a flat surface region a step lower thana rest flat surface region 120 separated by an edge 101 substantiallyalong a second direction x. The integrated coupler 301 is disposed nextto the edge 101 to couple with the tunable filter 200 formed in thesilicon photonics substrate 100 so that the wavelength tuning can beachieved through the tunable filter 200. The laser diode flip-chip 400is configured to be attached into the patterned region 110 to bond withthe bond pad 111 while rests against on the vertical stopper 112 and113. At the same time, the step section along the edge 101 also acts asan edge stopper against an end of the laser diode chip 400. Eventually,laser light that has been tuned by the tunable filter 200 is outputtedfrom an opposite facet of the laser diode chip 400. Referring to viaFIG. 1 and FIG. 3, the integrated coupler 302 can be used to couple thelaser output into a silicon wire waveguide in the same silicon photonicssubstrate 100 to deliver the laser light to either the receiver block3000 and the transmitter block 2000.

In a specific embodiment, the tunable filter 200 is configured as aVernier ring reflector filter. Optionally, the tunable filter 200 is aSi wire waveguide 220 fabricated in the silicon photonics substrate 100.Optionally, the tunable filter 200 is formed in the rest flat surfaceregion 120 beyond the patterned region 110. The Si wire waveguide 220includes at least two ring resonators 221 and 222. Optionally, the tworing resonators are made with slightly different radii. Optionally, afirst ring 221 is coupled to a reflector ring 223 which is also made bya linear section of the Si wire waveguide coupled to a ring-likestructure via a 1-to-2 splitter. Optionally, a second ring 222 iscoupled to the integrated coupler 300 via a linear wire waveguide 210made by different material. Optionally, the linear wire waveguide 210 isa SiN based waveguide formed in the same silicon photonics substrate100.

In the embodiment, the tunable filter 200 further includes a first ringheater (Ring1_HTR) 201 having a thin-film resistive layer overlying thefirst ring 221, a second ring heater (Ring2_HTR) 222 having a resistivethin-film overlying the second ring 222, and a phase heater (Phase_HTR)203 overlying the reflector ring 223. By changing temperature throughchanging voltages supplied to the two ring heaters (201 and 202),multiple resonate peak positions in transmission spectrum through eachof the two ring resonators (221 and 222) can be tuned. Since the tworings have different radii, there is an offset between the twotransmission spectra when they are superimposed (see FIG. 8). As they gothrough the reflector ring 223, a reflection light spectrum with astrong peak is produced (see FIG. 9) and tunable by changing temperaturethrough changing voltage supplied to the phase heater (203). Optionally,each heater is made by a resistive thin film geometrically covering eachring-shaped wire waveguide and terminated with two bond pads for bondingto an external power supply.

In the embodiment, the laser diode chip 400 includes a gain region. Thegain region includes an InP-based active region that is driven toproduce a laser light. The laser light, as it is initially generatedfrom the InP active region, is inputted via the integrated coupler 301and the linear wire waveguide 210 into the tunable filter 200. The lightwill pass through the at least two ring resonators 222 and 221 andreflected by the reflector 223 back to the gain region of the laserdiode chip 400. The reflectivity spectrum, as shown in FIG. 10, yields astrong peak of a laser light at a wavelength. The wavelength is tunablein a wide band range at least from 1560 nm to 1530 nm shown in FIG. 10by tuning the phase heater 203. The light is outputted as a laser lightat a fixed wavelength when the round-trip cavity lasing condition is metif an integral of a whole light path of the tunable laser device 10equals to N2π (N is an integer).

FIG. 4 is a schematic diagram showing a perspective view a laser diodechip flipped bonding to a silicon photonics substrate according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. Referring to FIG. 4, a section of a substrate 100 isshown to include a patterned region 110 out of rest flat surface region120. The patterned region 110 is configured to be a flat region being astep lower than rest flat surface region 120. Along one step an edgestopper 101 is formed facing a first direction z. Optionally, the stepis along a second direction x perpendicular to the first direction z. Onthe patterned region 110, there is a bond pad 111 formed along the firstdirection z. On both sides of the bond pad 111, there are two verticalstoppers 112 and 113 which are two thin plates having certain heights.Two extended parts 117 of the bond pad 111 are used for bonding with anexternal source. Further along these vertical stoppers, a plurality ofalignment features 115 are formed. Optionally, an alignment feature 115includes multiple fiducials lined in one or two rows along the firstdirection z.

In the embodiment, a laser diode chip 400 can be pre-fabricated with again region 410 and a metallic electrode 411 formed on top in anelongated shape. The gain region 410 is formed from one edge to anotherof the chip. Optionally, the metallic electrode 411 is formed to be incontact with a P-side layer of an active region made by InP-based P-Njunction quantum well structure. On two sides of the metallic electrode411, an alignment feature 415 is formed on the laser diode chip andconfigured to match the plurality of fiducials of the alignment feature115 on the patterned region 110. Referring to FIG. 4, the laser diodechip 400 is a flip chip bonded onto the patterned region 110 of thesubstrate 100. The configurations for both the patterned region 110 andthe laser diode chip 400 allow the latter is rest against the verticalstoppers 112 and 113 of the former with one edge of the latter againstthe edge stopper 101 of the former as the alignment feature 415 of thelatter is engaged with the plurality of fiducials 115 of the former.

FIG. 5 is an exemplary diagram of a wavelength tuning map of a siliconphotonics tunable laser according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown,the diagram is plotted as spectrum frequency 2D map varied with powerssupplied to two power supplies for the two ring heaters in the tunablefilter mentioned above. The dashed rectangle gives a possible tuningrange. As the two ring resonators are provided with different radii, iteffectively yields an extended tunable range for the spectrum wavelengthas the two transmission spectra are superimposed when the two ringresonators are physically coupled, for example, in a Vernier ring filterconfiguration (see FIG. 8). Optionally, the long side of the rectangleprovides a relative rough tuning range of wavelength for more than 50nm, e.g., from ˜1520 nm to 1575 nm, and the short side of the rectangleprovides a relative finer tuning range of wavelength for ˜10 nm, e.g.,from ˜1565 nm to ˜1575 nm.

FIG. 6 is a simplified diagram of a silicon photonics tunable laserdevice according to another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown, the tunable laserdevice 40 includes a first laser diode chip 430 bonded onto a firstpatterned region 410 of a substrate 100, a second laser diode chip 440bonded onto a second patterned region 420 of the substrate 100, atunable filter 470 coupled to a first gain region 435 of the first laserdiode chip 430 via a first integrated coupler 451 and coupled to thesecond gain region 445 of the second laser diode chip 440 via a secondintegrated coupler 460, a wavelength locker 480 configured to lock thewavelength of a reflected light from the second gain region 445 throughthe tunable filter 470, and a laser output is realized at an end facet432 of the first gain region 435 where a third integrated coupler 452can be employed for coupling the laser output to a silicon wirewaveguide. Referring to FIG. 1 and FIG. 6, the laser output from thetunable laser 1000 can be coupled via the integrated coupler 452 to awaveguide in the silicon photonics substrate 100 which further deliversto both the coherent receiver block 3000 and the coherent transmitterblock 2000 via waveguide through a power splitter 1001.

Referring to FIG. 3 and FIG. 6, each of the first laser diode chip 430and the second laser diode chip 440 of the tunable laser 40 issubstantially configured to be same as one laser diode chip 400 that hasa metallic electrode in contact with a P-type layer of correspondingactive region and is flipped down to have the metallic electrode bondedwith a bond pad of the first patterned region 410 and the secondpatterned region 420 in the same substrate 100. In particular, the firstlaser diode chip 430 is configured to be a cavity having a first endfacet 431 and a second end facet 432 with the gain region 435 as a wirewaveguide along an active region bounded between them. As the firstlaser diode is flipping (P-side down) bonded to the first patternedregion 410, the first end facet 431 is against an edge stopperassociated with the first patterned region 410 to be aligned with thefirst integrated coupler 451. The silicon wire waveguide associated withthe first gain region 435 is configured to be in a curved shape with anon-perpendicular angle relative to each of the first end facet 431 andthe second end facet 432 to reduce direct back reflection of the lightby the corresponding end facet. Optionally, the first end facet 431includes an anti-reflective coating. Optionally, the second end facet432 is also coated with an anti-reflective coating for facilitatinglaser output. The first laser diode chip 430 is driven by a driver togenerate a light as an input light into the tunable filter 470 via firstwaveguide 491. The second laser diode chip 440 is configured to be acavity having a third end facet 441 and a fourth end facet 442 with thesecond gain region as a silicon wire waveguide along an active regionbounded between them. As the second laser diode chip is flipping (P-sidedown) bonded to the second patterned region 420, the first end facet 441is against an edge stopper associated with the second patterned region420 to be aligned with the second integrated coupler 460. Optionally,the third end facet 441 is coated by an anti-reflective coating and thefourth end facet 442 is coated by high-reflective coating to enhancereflection of the input light. The reflected light can pass through thesecond integrated coupler 460 back to the tunable filter 470 via asecond waveguide 492 so that the cavity of the second gain region 445,in addition to provide gain to the reflected light, acts also as a ringreflector of the tunable filter in substantially a Vernier ringreflector configuration.

In the embodiment, the tunable filter 470 of the tunable laser 40 is aSi wire waveguide fabricated in the substrate 100 particularly in aregion 120 beyond the first patterned region 410 and the secondpatterned region 420. The tunable filter 470 includes two ringresonators, a first ring resonator 471 and a second ring resonator 472coupled to each other. The two ring resonators are coupled to the firstwaveguide 491 via a 2-to-1 coupler 473 and coupled to the secondwaveguide 492 via another 2-to-1 coupler 474. Optionally, the 2-to-1coupler is still in waveguide form with one port in one end and twoports in opposite end. Optionally, it is a splitter from one-port end totwo-port end or a combiner from two-port end to the one-port end. Boththe first waveguide 491 and the second waveguide 492 are fabricated inthe region 120 of the substrate 100 to couple respective with the firstintegrated coupler 451 and the second integrated coupler 460. The firstintegrated coupler 451 is disposed next to the edge stopper associatedwith the first patterned region 410. The second integrated coupler 460is disposed next to the edge stopper associated with the secondpatterned region 420. Optionally, each of the first waveguide 491 andthe second waveguide 492 is made by SiN material embedded in a Si-basedsubstrate 100. Optionally, the wire waveguide of the tunable filter 470is made by Si material.

Referring to FIG. 4, the tunable filter 470 of the tunable laser 40further includes a first heater (Ring1_HTR) having a resistive thin-filmoverlying the first ring resonator 471, a second heater (Ring2_HTR)having a resistive thin-film overlying the second ring resonator 472, athird heater (Phase_HTR) having a resistive thin-film overlying a phaseshifter section 475 of the Si wire waveguide that is connected with thesecond waveguide 492. These heaters are configured to change temperatureto cause a change of transmission spectrum of the light passing throughrespective ring resonators. Each transmission spectrum of the ringresonator has multiple resonate peaks (see FIG. 6). In an embodiment,the two ring resonators, 471 and 472, are provided with slightlydifferent radii, then an offset between the two transmission spectraexists when they are superimposed (see FIG. 6). The first heater and thesecond heater can be controllably change temperatures of the respectivefirst ring resonator and the second ring resonator to cause respectiveresonate peaks to shift to provide an extended tunable range of thewavelengths of those resonate peaks. After the input light passingthrough the tunable filter 470 is reflected back by the cavity of thesecond gain region 445, a reflectivity spectrum gives a stronger centralpeak (see FIG. 9), which is further tunable by changing temperature ofthe phase shifter section 475 using the third heater. In this case, thesecond gain region 445 acts as a ring reflector as the tunable filter470 is configured to be a Vernier ring reflector while the phase shiftersection 475 is formed next to the reflector instead of separated fromthe reflector as shown in FIG. 10.

Optionally, the tunable filter 470 of the tunable laser 40 includes afourth heater having a resistive thin-film overlying a section of onebranch of the 1-to-2 coupler 473 for finely balance power of input lightsplit from the first waveguide 491 into the two branches respectivelycoupled to two ring resonators 471 and 472.

In the embodiment, the wavelength locker 480 is configured to be a delayline interferometer (DLI) based on Si waveguide formed in the substrate100. Optionally, the wavelength locker 480 includes an input portcoupled via a splitter to the first waveguide 491 to receive thereflected light from the tunable filter 470. Optionally, one end of theinput port is a SiN waveguide coupled to the first waveguide 491 whichis also made by SiN material. Another end of the input port connects toa 1-to-2 splitter 481 to guide one part of the light into a monitor portPM0 and another part of the light into the DLI via another 1-to-2splitter 482. The light then comes out of the DLI via a 2-to-2 splitter483 to a first interference output port PM1 and a second interferenceoutput port PM2. In the embodiment, the wavelength locker 480 ispre-calibrated to set the DLI for locking the wavelength (of thereflected light from the tunable filter) to certain channel wavelengthsof a wide band. Optionally, the channel wavelengths supplied by thetunable laser 40 are ITU channels in C-band for DWDM application. Ofcourse, the disclosure of the tunable laser 40 can be applied to O-bandlight source for CWDM application. Optionally, the tunable laser 40 isintegrated in a coherent transceiver a coherent receiver block and acoherent transmitter block substantially on a same silicon photonicssubstrate (see FIG. 1). Optionally, each of the monitor port PM0, thefirst interference output port PM1, and the second interference outputport PM2 is terminated with a photodiode for measuring light power interms of photocurrent. A differential signal characterized by aphotocurrent difference between PM1 and PM2 over the sum of them iscollected to be an error signal fed back to drivers for the first laserdiode chip and the second laser diode chip to adjust wavelength oflight. Ideally, when the wavelength is adjusted or locked to a desiredITU channel pre-calibrated for the wavelength locker, the error signalshould be zero, i.e., PM1=PM2.

In another aspect, the present disclosure also provides a method fortuning wavelengths of a silicon photonics based tunable laser devicedescribed hereabove. FIG. 7 is a flowchart of a method for tuningwavelength of a laser output of the silicon photonics tunable laserdevice according to an embodiment of the present invention. As shown,the method includes a step of generating a light with a wavelength nearITU channels (for example, in C-band) in a dual-gain configurationincluding a first active region and a second active region. Referringback to FIG. 6, in a specific embodiment, a first laser diode chiphaving a first metallic electrode in contact with a P-type layer of thefirst active region is provided and a second laser diode chip having asecond metallic electrode in contact with a P-type layer of the secondactive region is provided. Further, the first laser diode chip to havethe first metallic electrode is flipping bonded with a bond pad in afirst patterned region of a substrate to align the first active regionto a first integrated coupler and the second laser diode chip to havethe second metallic electrode is flipping bonded with a bond pad in asecond patterned region of the substrate to align the second activeregion to a second integrated coupler. The first active region and thesecond active region is connected via the silicon photonics tunablefilter to form a combined resonate cavity. Referring to FIG. 7, themethod includes driving the first laser chip and the second laser diodechip to generate the light in the combined resonate cavity. Inparticular, the method includes a step of inputting the light with gainfrom a first active region of a first laser diode chip driven by itsdriver. The input light with gain from the first active region iscoupled into a first integrated coupler into the first waveguide whichguides the input light to the silicon photonics based tunable filter.Additionally, the input light from the first active region passesthrough the first integrated coupler via a first waveguide into thetunable filter and it further passes via a second waveguide and throughthe second integrated coupler into the second active region andreflected with additional gain therefrom, achieving dual gains throughthe round-trip path of the combined resonate cavity.

Referring to FIG. 7, the method further includes reflecting the lightwith additional gain from a second active region of a second laser diodechip. The reflected light with additional gain from the second activeregion further passes through the second integrated coupler and back tothe tunable filter via a second waveguide.

Additionally, the tunable filter is configured to have a first ringresonator Ring1, a second ring resonator Ring2, and a Phase shiftersection. The method further includes a step of setting respectively afirst heater associated with the first ring resonator, a second heaterassociated with the second ring resonator, and a third heater associatedwith the phase shifter to set the wavelength near an ITU channel.Respectively, the first heater, the second heater, and the third heaterare configured to be resistive thin-films formed in the substrate tocover at least partially the first ring resonator Ring1, the second ringresonator Ring2, and the Phase shifter section. Each of these heaterscan be controlled by voltages applied to two coupling electrodes from anexternal power supply. In a specific embodiment, the step includesreading voltages respectively set from the first heater, the secondheater, and the third heater from a preset look-up-table (LUT). Thevoltages read from the LUT are substantially correlated with thecorresponding ITU channel. For example, some specific voltage values arepreset for wavelength at 1535 nm in C-band. Further, the step includesapplying voltages read from the LUT respectively to the first heater andthe second heater to respectively set two transmission spectra of thefirst ring resonator and the second ring resonator to obtain asynthesized spectrum with a strong peak wavelength in an extendedtunable range. For example, the extended tunable range can be variedfrom 1520 nm to 1570 nm. In another example, when the gain profile isrelatively limited, the extended tunable range can be at least variedfrom 1535 nm to 1565 nm. Furthermore, the step includes applying avoltage read from the LUT to the third heater to set a phase of areflectivity spectrum with the strong peak wavelength in the extendedtunable range. The reflection spectrum is set substantially based on thesynthesized spectrum.

Referring to FIG. 7, the method further includes monitoringphotocurrents at a monitor port split from the input port, a firstinterference output port, and a second interference output port of thewavelength locker (see FIG. 6) based on the light reflected from thesecond active region and filtered by the tunable filter. Each of themonitor port, the first interference output port, and the secondinterference output port is respectively terminated with a photodiode(such as PM0, PM1, and PM2, see FIG. 6). Each of these photodiodesgenerates a photocurrent as a measurement of the light power thereof,which can be monitored in real time. An error signal based on adifferential light power between the first interference output port andthe second interference output port can be used as a feedback for tuninglight wavelength to be locked to a pre-calibrated wavelength, e.g., anITU channel.

Furthermore, the method includes tuning the first heater and the secondheater to coarsely tune the transmission spectrum through each of thefirst ring resonator and the second ring resonator until thephotocurrents at the first interference output port and the secondinterference output port are equal. Since slightly different radii areassigned for the first ring resonator and the second resonator, anoffset exists between the two transmission spectra. A synthesizedspectrum can be obtained by superimposed the two transmission spectra,which includes at least one strong peak as two transmission peaks of tworing resonators are falling to a same wavelength. By tuning both thefirst heater and the second heater, the position of this strong peak inthe synthesized spectrum is shifted in the extended tunable range. Whenthe photocurrents at the first interference output port and the secondinterference output port are equal, it means the peak wavelength issubstantially tuned to match a pre-calibrated wavelength locked by thewavelength locker as the error signal becomes zero. Of course, thewavelength locker 480 can be configured to in different manners forachieving the wavelength locking function in combination with thetunable filter 470 configured as a Vernier ring reflector. Many of thedifferent silicon-photonics-based wavelength locker configurations canbe referred to a U.S. Pat. No. 10,056,733 commonly assigned to InphiCorporation.

The method further includes tuning the third heater to finely tunereflection spectrum by maximizing the photocurrent of the monitor portof the wavelength locker representing a maximum gain from a round tripcavity lasing condition associated with both the first active region andthe second active region. The Phase shifter section of the tunablefilter is located at a straight section of Si wire waveguide outside thetwo ring resonators. When the third heater, which is placed at leastpartially over the Phase shifter section, is tuned to change temperatureof the Phase shift section, a phase of the reflected light can be tunedin accordance with the whole round-trip path of the light between thefirst active region and the second active region. The lasing conditionis a maximum gain obtained under the physical setup of the optical pathbetween the first active region and the second active region and phaseoptimized by the Phase shift section, which is characterized by themaximum power measured by photocurrent at the monitor port of thewavelength locker. The enlarged cavity with two active regions over asingle active region certainly enhances lasing power of the tunablelaser device.

FIG. 8 is an exemplary diagram of two superimposed transmission spectraof respective two ring resonators with different radii of a tunablefilter in the silicon photonics tunable laser device according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. As shown, each transmission spectrum of a ring resonatorcontains multiple peaks with a certain spacing depended on the radius ofthe ring. Since, two different radii are provided for Ring1 and Ring2,which results in two different spectra-free-ranges (SFRs), there is anoffset between the two transmission spectra. Yet, two specific peaksrespectively from the two transmission spectra may fall to asubstantially common wavelength, for example, ˜1540 nm.

FIG. 9 is an exemplary diagram of a reflectivity spectrum of a reflectorcoupled to the two ring resonators of the tunable filter according tothe embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. After the two transmission spectra are superimposedas light passing the two ring resonators is recombined in the singlestraight section of the wire waveguide and reflected from the secondactive region, a reflection spectrum is obtained which is substantiallybased on a synthesized spectrum of the two transmission spectra. Asshown, the reflection spectrum is characterized by at least one strongpeak at a wavelength, e.g., ˜1540 nm.

FIG. 10 a simplified block diagram of the tunable filter including tworing resonators, a reflector, plus a phase shifter in a Vernier ringreflector configuration according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown,the tunable filter includes three sections: two ring resonators andphase control sections. The two ring resonators have slightly differentFSRs, which allows for extension of the tuning range to the lowestcommon multiple of the FSRs through the Vernier effect. One phasecontrol section is a loop reflector formed by a loop waveguide and adirectional coupler. Optionally, the loop reflector can be replaced by acavity facet of another laser diode chip. Another phase control sectioncan be simply a section of waveguide with an added heater for directlytuning phase based on thermal optical effect. A reflection spectrum issubstantially a synthesized spectrum obtained by superimposing two ringspectra. External laser cavity is configured between the facet of the(first laser diode chip) active region and a loop reflector. When thepeaks of the transmission spectrum through the rings are identical andthe phase is adjusted on the peak of the rings, lasing operation isoccurred. Of course, there are multiple variations of the tunable filterconfiguration in terms of a setup of the ring resonators and phasecontrol sections, resulting different synthesized spectrum.

FIG. 11 is an exemplary diagram of two synthesized spectra respectivelycorresponding to wavelengths being tuned from 1555 nm to 1535 nm bytuning the tunable filter in Vernier ring reflector configuration andcorresponding gain profile from 1530 nm to 1570 nm according to theembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. As shown, the synthesized spectrum is characterized by astrong peak due to superimposing two transmission spectra with commonmultiple peak wavelength for different SFRs. The peak position, orwavelength value, can be tuned by tuning the Vernier ring reflectoraround an optimal central position in an extended tunable range.

FIG. 12 is an exemplary diagram of laser spectra outputted by thesilicon photonics tunable laser device with laser wavelength being tunedfrom 1555 nm to 1535 nm according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown,the laser wavelength is indicated by the peak of the spectra, which canbecome tunable across C-band (or other wide band) by tuning the Vernierring reflector response. In the example, the laser wavelength is tunedfrom 1555 nm to 1535 nm. The tunable filter based on Vernier ringreflector configuration acts as wavelength selective filter for the gainprofile. The center or optima position of the gain profile can beinitially preset by setting the optimal temperatures usingpre-calibrated voltages supplied to the resistive heaters associatedwith the Ring1, Ring2, and Phase shift section. For example, thepre-calibrated voltages can be stored in a look-up-table of a memory,which can be read every time for initialing the silicon photonics basedtunable laser device. Coarse wavelength tuning can be achieved bychanging temperatures around the Ring1 and the Ring2 to tune thewavelength in an extended tunable range around the optimal gain profileposition set by the initial settings of the heaters associated with theRing1, Ring2, and the Phase shift section. Fine wavelength tuning can bedone by changing temperature around the Phase shift section. The laserregions also have a wavelength dependent gain profile which is muchwider than those from the rings.

FIG. 13 is a schematic diagram of three types of an integrated couplerbased on SiN in Si waveguide according to some embodiments of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Likethe FSRs, the coupling coefficients of the tunable filter with two ringresonators are important parameters in order to achieve large modalgain-difference for obtaining enough high side-mode suppression ratio toother modes. One key factor to determine the coupling coefficient is thealignment of light mode confined in the integrated coupler with theincoming laser light beam. On the other hand, tolerance to misalignmentexisted with different integrated coupler designs would be an advantagefor enhance productivity of the tunable laser device.

Referring to FIG. 13, a first type of integrated coupler design is anInverse Nanotaper structure made by SiN material embedded in a Siwaveguide with a sharp needle pointing toward a waveguide end. A smallmode diameter is shown for this design, giving large coupling loss inresponse to a relatively small misalignment. A second type of integratedcoupler design is a Trident structure made by SiN material embedded in aSi waveguide. The SiN Trident structure includes an SiN nanotapersandwiched in partial length laterally by two SiN symmetrical nanotapersthat are extended up to the waveguide end of the coupler. A large modediameter for this design is shown, giving lower coupling loss induced bymisalignment. A third type of integrated coupler design is a Forkstructure made by SiN material embedded in a Si waveguide. The Forkstructure includes a SiN nanotaper sandwiched in full length laterallyby two SiN linear stripes up to the waveguide end. It has a medium sizedmode diameter yet giving a smallest coupling loss especially for smallermisalignment between the light mode and the laser spot.

FIG. 14A is an exemplary diagram of a relationship between coupling lossand a lateral misalignment for an integrated coupler coupled between thetunable filter and a laser diode chip according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Asshown, SiN Trident and SiN Fork type integrated couplers offset lowercoupling loss alternative to SiN Inverse Nanotaper type integratedcoupler with comparable tolerance to misalignment in lateral axisbetween a laser beam coming out of the laser diode chip and modediameter of the integrated coupler. In the example, the coupling lossfrom mode mismatch based on 2.5 μm laser diode spot size. FIG. 14B is anexemplary diagram of a relationship between coupling loss and a verticalmisalignment for the integrated coupler coupled between the tunablefilter and a laser diode chip according to the embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown,SiN Trident and SiN Fork type integrated couplers offset lower couplingloss alternative to SiN Inverse Nanotaper type integrated coupler withcomparable tolerance to misalignment in vertical axis between a laserbeam coming out of the laser diode chip and mode diameter of theintegrated coupler. Additionally, the SiN Fork type integrated coupleroffers more compact design than SiN Trident type integrated coupler withlower coupling loss (e.g., less than 1 dB). In an example, the Fork typeintegrated coupler has just half length of the Trident type integratedcoupler. In an example, the coupling loss for the Fork type is just halfof that for Trident type when the mis-alignment is less than 0.6 μm inboth lateral or vertical direction.

In an embodiment, the coherent optical transceiver is integrated in asingle chip. FIG. 15A shows a perspective view of a coherent opticaltransceiver chip is integrated on a silicon photonics substrate. FIG.15B shows a side view of the coherent optical transceiver chip.Referring to FIG. 15A, a silicon photonics substrate 100 is provided itstop surface as a substrate for integrating all components of a coherentoptical transceiver chip 5000. The coherent optical transceiver chip5000 has a fiber-coupler 520 configured to hold a first fiber 511 and asecond fiber 512 respectively coupled with the silicon photonicssubstrate 100. The coherent optical transceiver chip 5000 includes atunable laser device 1000 including two laser diode (LD) chips, a firstLD 430 and a second LD 440, both flip-mounted onto a first region of thesilicon photonics substrate 100. Both LD chips 430 and 440 are coupledwith a wavelength tunable section embedded in the first region asdepicted in the FIG. 15A. The tunable laser device 1000 is substantiallysimilar to the tunable laser 40 shown in FIG. 6. The two laser diodechips 430 and 440 are configured to have p-side electrodes of respectivetwo gain regions (referred to 430 and 440 too) facing down to mount onthe silicon photonics substrate 100. The substrate 100 is prepatternedwith a plurality of surface fiducials, vertical stoppers, edge stoppers,and bond pads for mounting and aligning the LD chips. The mounting ofthe LD chips 430 and 440 allows respective backend facets of the twogain regions to be aligned optically with the wavelength tuning filter470 and a wavelength locker 480. At the same time, the mounting of theLD chip 430 allows its front-end facet of the first gain region tooutput the laser light coupled into a waveguide that leads to a siliconphotonics circuit. Optionally, the wavelength tunable filter 470 and thewavelength locker 480 are directly made by wire waveguides in the firstregion of the silicon photonics substrate 100. Optionally, they are madeby silicon and silicon related materials embedded into the siliconphotonics substrate 100. In particular, the wavelength locker 480includes a delay-line interferometer and multiple optical power monitorsmade by silicon or silicon nitride waveguides. The wavelength tunablefilter 470 includes two or more micro-ring resonator waveguides 471 and472 followed by linear waveguides 491 and 475 respectively coupled tothe first gain region 430 and the second gain region 440. The two ormore ring resonators have slightly different radii to allow a lightcoupled from the two gain regions being reflected therein multiple timeswith at least 90% reflectivity and being tuned in an extended wavelengthrange of synthesized spectrum by at least one resistive heater partiallyoverlying each of the two or more micro-ring resonator waveguides and aheater overlying a section of linear waveguide 475 as a phase shifter.Optionally, the power supplies for the resistive heaters and LD driverare provided through electrical connections embedded in the substrate100 and multiple through-silicon vias (TSVs) in the substrate 100 toconnect with some of conducting bumps of the board grid array (BGA) at abottom surface of the substrate 100 (as seen in FIG. 15B).

In the embodiment, the coherent optical transceiver chip 5000 furtherincludes a transimpedance amplifier (TIA) chip 3400 flip-mounted on asecond region of the silicon photonics substrate 100. The TIA chip 3400is electrically coupled to corresponding electrical connections embeddedin the substrate 100 or through some TSVs connected to BGA at the bottomsurface of the substrate 100. A printed circuit board (PCB) can be usedto mount the silicon photonics substrate 100 to provide desiredelectrical connection for the TIA chip for operating the opticaltransceiver 5000. Optionally, the TIA chip 3400 is configured to preparesome voltage signals converted from some hybrid current signals detectedfrom incoming coherent light signals. Additionally, the coherent opticaltransceiver chip 5000 includes a driver chip 2600 flip-mounted on athird region of the silicon photonics substrate 100. The driver chip2600 is electrically coupled to corresponding electrical connectionsembedded in the substrate 100 or through some TSVs connected to BGA atthe bottom surface of the substrate 100, and to utilize the PCB forcompleting the electrical connections.

Furthermore, the coherent optical transceiver chip 5000 includes asilicon photonics circuit integrated with the tunable laser device 1000,the TIA chip 3400 and the driver chip 2600. The silicon photonicscircuit is directly formed in a fourth region of the silicon photonicssubstrate 100 which is substantially sunken into the substrate 100.Optionally, the silicon photonics circuit includes several siliconphotonics devices respectively formed in different geometrical portionsof the fourth region. Functionally, as shown in FIG. 1, the siliconphotonics circuit includes mainly a receiver block 3000 and atransmitter block 2000. Referring to FIG. 1 and FIG. 15A, the receiverblock 2000 is configured to have a waveguide (not explicitly shown)coupled with the first fiber 511 to receive a coherent input lightsignal and to have another waveguide (not explicitly shown) coupled withthe tunable laser device 1000 to receive a first portion of a laserlight as local oscillator signals to assist detections of both TM-modeand TE-mode light signals in the coherent input light signal by the TIAchip 3400. The transmitter block 2000 is configured to use the driverchip 2600 to drive modulations of a second portion of the laser lightfrom the tunable laser device 1000 to generate a coherent output lightsignal outputted to the second fiber 512.

Referring to FIG. 15A, although no details are explicitly shown, thesilicon photonics circuit includes a first power splitter 1001 formed inthe substrate 100 having an input waveguide 1010 coupled and aligned tothe front-end facet of the first gain region 430 to receive the laserlight outputted therefrom. The first power splitter 1001 is configuredto split the laser light to two portions, a first portion outputted to afirst output waveguide 1011 and a second output waveguide 1012 with anX:Y ratio ranging from 10:90 to 50:50. The silicon photonics circuitincludes a sub-circuit having at least a polarization beam splitterrotator (PBSR), a second power splitter, and a pair of opticalreceivers, configured as a receiver block 3000 shown in FIG. 1,integrated in one sub-region 3101 of the fourth region in the siliconphotonics substrate 100. Functionally, the polarization beam splitterrotator 3100 has an input waveguide directly coupled to the first fiber511 at an edge of the silicon photonics substrate 100 to receive acoherent input light signal. The PBSR 3100 is configured as a shapedsilicon waveguide (see FIG. 2A) to receive the coherent input lightsignal and output the TE-mode light signal of the coherent input lightsignal and a TM*-mode light signal to two separate optical pathsrespectively fed to the two 90° hybrid optical receivers 3200 and 3300.The TM*-mode light signal is essentially a TE-mode light signal rotated90° from the TM-mode light signal of the coherent input light signal.The second power splitter 3001 is essentially a 3 dB coupler to splitthe first portion of the laser light coming from the first outputwaveguide 1011 of the first power splitter 1001 to two equal halves.Each half of the laser light is used as a local oscillator signalinputted to a respective one of the two 90° hybrid optical receivers3200 and 3300 to combine with the respective TE- and TM*-mode lightsignal to form a first hybrid light signal and a second hybrid lightsignal. Correspondingly, the two 90° hybrid optical receivers 3200 and3300 includes photo diodes configured to respectively convert the firsthybrid light signal and a second hybrid light signal to a first hybridcurrent signal and a second hybrid current signal.

Referring to FIG. 15A, the silicon photonics circuit also includes apolarization beam rotator combiner (PBRC) and a pair of opticalmodulators configured as a transmitter block 2000 shown in FIG. 1,integrated respective two sub-regions 2301 and 2302 of the fourth regionin the silicon photonics substrate 100. Particularly, each of the pairof optical modulators includes a silicon-waveguide based Mach-Zehnderinterferometer configured as in-phase/quadrature-phase modulator havingone in-phase branch and one quadrature-phase branch with a 90° phaseshifter, each branch being biased by voltages provided from the driverchip 2600 to drive modulations to light received from the second portionof the laser light coming from the second output waveguide 1012 of thefirst power splitter 1001 and passing through the silicon waveguides ofthe modulator itself. Each modulator is configured to output a modulatedlight signal with I/Q four-level modulations substantially in TE-modepolarization originated from the laser light from the tunable laserdevice 1000. The PBRC 2200 is coupled to the twoin-phase/quadrature-phase modulators to receive the two TE-modemodulated light signals, output one retaining the TE-mode modulatedlight signal while another one being rotated to a TM-mode modulatedlight signal, and combine the TE-mode modulated light signal with theTM-mode modulated light signal to a coherent modulated light signal.Referring to FIG. 15A, the silicon photonics circuit further includes apolarization-independent semiconductor optical amplifier (PI-SOA) 2100as a chip flip-mounted on the silicon photonics substrate 100 near anedge to couple with the PBRC 2200 at one end and couple with the secondfiber 512 at an opposite end. The PI-SOA 2100 is configured to provide awide range of output power of the coherent modulated light signal.Further, the PI-SOA 2100 delivers the amplified coherent light signal tothe second fiber outputted to the output port as a coherent output lightsignal.

FIG. 15B shows a side view of the coherent optical transceiver chip 5000of FIG. 15A. As shown, the coherent optical transceiver 5000 isintegrated on the single silicon photonics substrate 100. The siliconphotonics substrate 100 is a silicon photonics chip comprisingwaveguides made by silicon-related materials formed in asilicon-on-insulator substrate. A top surface of the silicon photonicssubstrate 100 is configured to allow multiple functional chips like TIAchip 3400, driver chip 2600, laser diodes chip 430 and 440, andsemiconductor optical amplifier 2100 to be mounted at respectiveregions. Optionally, each of these chips is flip-mounted with conductivebumps 170 facing down to bound with pre-formed bumps on the respectiveregions. Optionally, a plurality of conductive through-silicon vias canbe formed through the silicon photonics substrate 100 and filled withconductive materials for connecting those chips mounted on top thereofto some of board grid array 160 at bottom thereof. Optionally, the boardgrid array 160 is designed for mounting this integrated coherent opticaltransceiver 5000 on the silicon photonics substrate 100 onto a printedcircuit board in a modular package.

In another aspect, the present disclosure provides a compact package foran integrated coherent optical transceiver formed on a single siliconphotonics chip. FIG. 16A is a schematic diagram of an open package of anintegrated coherent optical transceiver according to an embodiment ofthe present invention. FIG. 16B shows a closed package of the integratedcoherent optical transceiver of FIG. 16A according to the embodiment ofthe present disclosure. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications. Asshown, the closed package 6000A is a fully cased coherent opticaltransceiver. The open package 6000 is with a lid member 150 beingremoved. The package 6000 includes an integrated coherent opticaltransceiver 5000 mounted on a printed circuit board (PCB) 600 in a metalcase. The metal case is, in addition to the lid member 150, assembledtogether with a pair of side members 140 naturally connected by a jointmember 141 near a front-end region of the case and a bottom member 130extending the joint member 141 to a back end 131 of the case. The pairof side members 140 has a pair of clip structures 145 to couple with thelid member 150. The PCB 600 has its board body supported on the bottommember 130 with multiple conductive pins 610 formed at an end region ofthe board body substantially located at the back-end region 131 of thecase. The package includes a first optical connector receptor 501configured as an input port and a second optical connector receptor 502configured as an output port for the transceiver 6000. Both input portand the output port are located on the joint member 141 before the frontend of the PCB board body 600.

The integrated coherent optical transceiver on the silicon photonicssubstrate 100 is substantially the coherent optical transceiver chip5000 shown in FIG. 15A. Details of the coherent optical transceiver chip5000 can be found in several earlier paragraphs. The first opticalconnector receptor 501 has its back end coupled with a first fiber 511and the second optical connector receptor 502 has its back end coupledwith a second fiber 512, both being held by a fiber-coupler 520 torespectively couple and optically align with an input waveguide into asilicon photonics circuit built in the silicon photonics substrate 100and an output waveguide connected from a polarization-independentsemiconductor optical amplifier (PI-SOA) 2100. Optionally, the firstoptical connector receptor 501 has its front end configured to mate withan optical connector connected to an input fiber delivering a coherentinput light signal with mixed TE- and TM-mode from an opticalcommunication system. The second optical connector receptor 502 has itsfront end configured to mate with an optical connector connected to anoutput fiber for outputting a coherent output light signal withfour-level I/Q modulation in both TE-mode and TM-mode polarizations.Depending on applications, the integrated coherent transceiver package6000A can be configured with a compact form factor that adapts with anysystem design for coherent optical communication.

In an alternative aspect, the present disclosure provides a light enginedevice including an optical coherent transceiver integrated on asemiconductor substrate member. For example, the optical coherenttransceiver is provided as the integrated coherent optical transceivershown in FIG. 1. For example, the substrate member is provided as onelike the substrate 100 of FIG. 15B. The light engine device includes asubstrate member comprising a surface region. The light engine devicefurther includes an optical input configured to an incoming fiber deviceand an optical output configured to an outgoing fiber device.Additionally, the light engine device includes a transmit path providedon the surface region. The transmit path includes a polarizationindependent optical amplifier device coupled to the optical output. Thetransmit path also includes a polarization beam rotator combiner devicecoupled to the polarization independent optical amplifier and coupled tothe optical output. The transmit path further includes a dualpolarization I/Q Mach Zehnder modulator device coupled to thepolarization beam rotator combiner device and coupled to the opticaloutput. The transmit path again includes a driver device coupled to thedual polarization I/Q Mach Zehnder modulator device and configured todrive an electrical signal to the dual polarization I/Q Mach Zehndermodulator. Furthermore, the transmit path includes a tunable laserdevice comprising a laser diode chip having a gain region with a p-sideelectrode flipped down and mounted on the substrate member. The gainregion is coupled with a wavelength tuning section formed in thesubstrate member to tune wavelengths of a laser light outputted from thegain region to a waveguide in the substrate member. Moreover, thetransmit path includes a first power splitter coupled to the waveguideto split the laser light to a first light and a second light. The secondlight is coupled to the dual polarization I/Q Mach Zehnder modulatordevice. Further, the light engine device also includes a receive pathprovided on the surface region. The receive path includes a second powersplitter coupled to the first light. The receive path further includes apair of 90° hybrid receivers. Each of the pair of 90° hybrid receiversincludes a photo detector device and a hybrid mixer device, coupledrespectively to two outputs of a polarization beam splitter rotator inthe substrate member to receive the optical input and to two outputs ofthe second power splitter to receive the first light from the tunablelaser device for assisting detections of a transverse electric (TE) modesignal and a transverse magnetic (TM) mode signal in the coherent inputsignal. Furthermore, the receive path includes a transimpedanceamplifier coupled to each of the 90° hybrid receivers and coupled toeach of the photo detector devices that convert a combination of thefirst light with the optical input into an electrical signal to betransmitted to using the transimpedance amplifier device. The lightengine device further includes a heterogeneous integration configuredusing the substrate member, the transmit path, and the receive path toform a single silicon photonics device.

Optionally, the substrate member comprises a silicon substrate.Optionally, the transimpedance amplifier is made of a silicon germaniumbipolar technology. Optionally, the transimpedance amplifier is made ofa silicon CMOS technology. Optionally, the transimpedance amplifier ismade of an indium phosphide technology. Optionally, the transimpedanceamplifier is made of a gallium arsenide containing technology.Optionally, the data center is configured for a social networkingplatform, an electronic commerce platform, an artificial intelligenceplatform, or a human tracking platform. Optionally,

Optionally, the light engine device is coupled to a major substratemember. The major substrate member, for example, provided as a circuitboard 600 of FIG. 16A, is configured to mount the light engine device, adigital signal processing device coupled to the light engine device, apower supply coupled to the light engine device and the digital signalprocessing device, a micro-controller device coupled to the light enginedevice to provide one or more controls using one or more control signalsto the light engine device, an electrical input and output configured tothe light engine device, the digital signal processing device, the powersupply, and the micro-controller device; and a mechanical and electricalconfiguration including the light engine device, the digital signalprocessing device, the power supply, the micro-controller device, andthe electrical input and output configured to the light engine device,the digital signal processor device, the power supply and themicro-controller device.

Optionally, the light engine device and the major substrate member areconfigured as a pluggable device. Optionally, the light engine deviceand the major substrate member together are configured on a system boardmember of a communication system intended for data transmitting andreceiving. Optionally, the system board member is provided in a switchsystem apparatus, the switch system apparatus being spatially disposedin a data center. Optionally, the data center is configured for a socialnetworking platform, an electronic commerce platform, an artificialintelligence platform, or a human tracking platform. Optionally, thedata center is coupled to a plurality of data centers spatially locatedthroughout a geographical region. Optionally, the data center is ownedby a commercial company or a government entity.

Optionally, the digital signal processing device includes a hostinterface to a switch device and a line interface to the light enginedevice.

Optionally, the major substrate member includes an electrical interfaceto the system board member, an optical interface to the system boardmember, and a mechanical interface to the system board member.Optionally, the mechanical interface is thermally configured using anattachment device to the system board member using a thermal interfaceregion coupled to the attachment device.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A light engine device comprising an opticalcoherent transceiver integrated on a semiconductor substrate member, thelight engine device comprising: a substrate member comprising a surfaceregion; an optical input configured to an incoming fiber device; anoptical output configured to an outgoing fiber device; a transmit pathprovided on the surface region and comprising: a polarizationindependent optical amplifier device coupled to the optical output; apolarization beam rotator combiner device coupled to the polarizationindependent optical amplifier and coupled to the optical output; a dualpolarization I/Q Mach Zehnder modulator device coupled to thepolarization beam rotator combiner device and coupled to the opticaloutput; a driver device coupled to the dual polarization I/Q MachZehnder modulator device and configured to drive an electrical signal tothe dual polarization I/Q Mach Zehnder modulator; a tunable laser devicecomprising a laser diode chip having a gain region with a p-sideelectrode flipped down and mounted on the substrate member, the gainregion being coupled with a wavelength tuning section formed in thesubstrate member to tune wavelengths of a laser light outputted from thegain region to a waveguide in the substrate member; a first powersplitter coupled to the waveguide to split the laser light to a firstlight and a second light, the second light being coupled to the dualpolarization I/Q Mach Zehnder modulator device; a receive path providedon the surface region and comprising: a second power splitter coupled tothe first light; a pair of 90° hybrid receivers, each of which comprisesa photo detector device and a hybrid mixer device, coupled respectivelyto two outputs of a polarization beam splitter rotator in the substratemember to receive the optical input and to two outputs of the secondpower splitter to receive the first light from the tunable laser devicefor assisting detections of a transverse electric (TE) mode signal and atransverse magnetic (TM) mode signal in the coherent input signal; and atransimpedance amplifier coupled to each of the 90° hybrid receivers andcoupled to each of the photo detector devices that convert a combinationof the first light with the optical input into an electrical signal tobe transmitted to using the transimpedance amplifier device; and aheterogeneous integration configured using the substrate member, thetransmit path, and the receive path to form a single silicon photonicsdevice.
 2. The light engine device of claim 1 wherein the substratemember comprises a silicon substrate.
 3. The light engine device ofclaim 1 wherein the transimpedance amplifier is made of a silicongermanium bipolar technology or a silicon CMOS technology or an indiumphosphide technology or a gallium arsenide containing technology.
 4. Thelight engine device of claim 1 wherein the light engine device iscoupled to a major substrate member, the major substrate membercomprising: the light engine device; a digital signal processing devicecoupled to the light engine device; a power supply coupled to the lightengine device and the digital signal processing device; amicro-controller device coupled to the light engine device to provideone or more controls using one or more control signals to the lightengine device; an electrical input and output configured to the lightengine device, the digital signal processing device, the power supply,and the micro-controller device; and a mechanical and electricalconfiguration including the light engine device, the digital signalprocessing device, the power supply, the micro-controller device, andthe electrical input and output configured to the light engine device,the digital signal processor device, the power supply and themicro-controller device.
 5. The light engine device of claim 4 whereinthe light engine device and the major substrate member are configured asa pluggable device.
 6. The light engine device of claim 4 wherein thelight engine device and the major substrate member are configured on asystem board member.
 7. The light engine device of claim 6 wherein thesystem board member is provided in a switch system apparatus, the switchsystem apparatus being spatially disposed in a data center.
 8. The lightengine device of claim 7 wherein the data center is configured for asocial networking platform, an electronic commerce platform, anartificial intelligence platform, or a human tracking platform.
 9. Thelight engine device of claim 7 wherein the data center is coupled to aplurality of data centers spatially located throughout a geographicalregion.
 10. The light engine device of claim 7 wherein the data centeris owned by a commercial company or a government entity.
 11. The lightengine device of claim 4 wherein the digital signal processing devicecomprises a host interface to a switch device and a line interface tothe light engine device.
 12. The light engine device of claim 6 whereinthe major substrate member comprises an electrical interface to thesystem board member, an optical interface to the system board member,and a mechanical interface to the system board member and is thermallyconfigured using an attachment device to the system board member using athermal interface region coupled to the attachment device.